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Browsing OU - Oklahoma Transportation Resources / Oklahoma Transportation Library by Author "Ahmed, Samir A."
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Item Open Access Components of variability in bituminous concrete pavement construction Volume I - Summary of current state practices (FHWA-OK-92-07) 2179(1992-6) Ahmed, Samir A.; Oklahoma Department of Transportation. Materials and Research Division. Office of Research & ImplementationThe Oklahoma Department of Transportation (ODOT) turned to quality assurance specifications in 1989 after several years of careful study and consideration. The objective of phase-I of this research project was to evaluate the ODOT's Quality Assurance Specifications (QAS) for bituminous concrete pavements in comparison with those developed by other states. To meet the objectives of this phase, a survey of practice was conducted in Fall 1990. A letter was mailed to state DOTs asking whether the agency is using statistically‡based QAS for bituminous concrete pavement construction, and if so, the letter requested copies of the specifications. Of the 30 state DOTs which responded to the survey, 70% had statistically-based QAS, 17% reported the use of combination of method specifications and QAS, and 13% were in the process of developing QAS or planning to develop one. High levels of satisfaction with, and confidence in, QAS were expressed by many of the agencies which used them. Results of the survey indicated that there was a wide variation among specifying agencies in the quality attributes used for acceptance purposes, definition of lot and sublot of bituminous pavement, decision rule for acceptance, allowable tolerances for acceptable construction, and the basis for payment. For acceptance purposes, the three most often used quality attributes were aggregate gradation, asphalt content. and in-place density. The two most common decision rules for acceptance were the percent within limits method and the average deviation method. The methods used to detennine the payment for a lot of construction material varied significantly among the different agencies.Item Open Access Components of variability in bituminous concrete pavement construction Volume II - Field and laboratory evaluation (FHWA-OK-92-07) 2179(1992-6) Ahmed, Samir A.; Oklahoma Department of Transportation. Materials and Research Division. Office of Research & ImplementationThe objectives of phase-II of the project were: 1) to detennine the components of the total variability in the measured quality attributes of acceptable bituminous concrete pavement construction in Oklahoma, 2) to assess the ODOT's specification tolerances for bituminous concrete pavement construction, 3) to evaluate the accuracy of the nuclear density gauge, and 4) to correlate the results of the nuclear test method for asphalt content detennination with those obtained using the solvent extraction method. To meet these objectives, a research plan consisting of literature review, statistical experimental design, field sampling, and laboratory testing was adopted. Random sampling was conducted both at the production plant and the roadway independent of acceptance and job control sampling. Testing was perfonned in the materials laboratories of the different ODOT Divisions. ANOV A results indicated that sampling and testing variances represent a significant portion of the total observed variance in the measured quality attributes of bituminous concrete pavement construction. The computed percentages within QNQC specification tolerances indicated that the present tolerances are practical and defensible. Correlations between density measurements obtained from the nuclear gauge and core samples ranged from 0.49 to 0.84. The use of calibrated relationships though regression analysis improved the estimation of core densities from nuclear measurements. Variability due to sampling and testing was largerin the core method than the nuclear gauge method. The correlation coefficient between individual asphalt content measurements using the extraction method and the nuclear gauge method was 0.63. No significant difference was found between the average asphalt content obtained from the extraction method and the average asphalt content obtained using the nuclear gauge method. Testing variability was less with the nuclear gauge method than the solvent extraction method.Item Open Access Evaluation of retroflective sheetings for use on roadway traffic signs (FHWA-OK-95-02) 2193(1994-9) Ahmed, Samir A.; Oklahoma Department of Transportation. Materials and Research Division. Office of Research & ImplementationThe primary objectives of this research were to evaluate the ODOT's policy on use of retroreflective sheeting products, and to identify any necessary changes to this policy based on driver visibility needs, durability of sk.eting materials, life-cycle cost, and other practical considerations. 1be scope of the study included three types of retroreflective sheetings (engineering grade, super-engineering grade. and encapsulated-lens highintensity sheeting), five sheeting colors (white, red, yellow, green. and blue) , and two sign fabrication metOOds (screening and overlay). To meet the objectives of this project, a research plan consisting of literature review, controlled field experiments, survey of ODOT field divisions, durability data collection and analysis, and lifecycle cost analysis was adopted. 1be findings of this study suggest that the specification of type ill-A (high-intensity, encapsulated glassbead sheeting) on all red and yellow signs, as well as green and blue signs on interstate highways and freeways is soum and defensible. 1be requirement that type II-A (super-engineering grade sheeting) be used on all other traffic signs, except orange colored signs, needs to be examined. Altlx>ugh the initial cost of sign face fabrication for type-mA sheeting is 25% to 65% higher than that of type-II.A, life-cycle cost analysis indicates that type-mA is more cost-effective than type-IIA Evidence from visibility distance analyses and subjective evaluations made by the test subjects suggests that, in addition to upgrading sign materials to provide greater luminance, larger sign size and letter size are needed to satisfy the minimum required visibility distances, particularly at high speed, high traffic volume, and high visual comp lexity locations.Item Open Access Evaluation of retroreflective sheetings for use on traffic control devices at construction work sites (FHWA-OK-91-06) 2177(1991-6) Ahmed, Samir A.; Oklahoma Department of Transportation. Materials and Research Division. Office of Research & ImplementationThe overall objective of this project was to evaluate the relative adequacy of the engineering grade, super-engineering grade, and high-intensity grade sheetings when used on traffic control devices at construction work zones. Evaluation criteria included driver visibility needs, durability and economics, and other practical considerations. To meet the objectives of this project, a research plan consisting of literature review, controlled field experiments, real-world field experiments, accelerated weathering tests, survey of Oklahoma traffic control contractors, and economic analysis was adopted. The results of these tasks formed the basis for the findings and conclusions of this study. While the high-intensity grade sheeting has the highest target value of the three sheeting grades, the tradeoff between detection and legibility of traffic control signs was interpreted to favor the use of the super-engineering grade on signs in both urban and rural construction projects. Durability, economics, and other practical issues emphasized by traffic control contractors support this conclusion. Nevertheless, use of the high-intensity grade sheeting in urban construction projects may be warranted at locations with visual clutter and excessive background lights. The beneficial effects of upgrading the type of sheeting used on barrels, barricades, and vertical panels from engineering grade to high-intensity grade or super-engineering grade were demonstrated by the significant increase in both the detection and recognition distances of these devices. Yet, the benefits of upgrading to the high-intensity grade were found to be offset by the significant increase in cost, the less durability of the sheeting material, and the problems with fabrication and handling. Upgrading to super-engineering grade offers the most cost-effective and balanced solution.